Physical-chemical techniques and mutant methodology will be employed to study the structural basis for the establishment of the stereospecific sites in the regulatory protein biosynthetic L-threonine deaminase from Salmonella typhimurium. The in vivo and in vitro regulation of the expression of the isoleucine-valine genes of S. typhimurium will be studied. The in vivo study will follow upon isolating these genes on an amplifiable plasmid and will be aimed at assessing the propriety of regulation in linear vs. superhelical DNA templates.